This application claims priority of French patent Application No. 00 06771, filed on May 26, 2000.
The present invention relates to ellipsometric metrology for a sample contained in a chamber or the like in order to obtain measures which are non-destructive of the state of the surface of the sample, without removing the sample from the chamber.
It is applied in general in the optical characterisation of a sample, and more particularly to a sample of thin semi-conducting layers. It is therefore applied in the sequence of production of integrated circuits.
Generally, ellipsometry is used to measure in real time and in-situ a surface change in the course of a manufacturing process of integrated circuits, e.g. during the growth of layers on a substrate.
In a known manner, an ellipsometry apparatus directs a polarised illuminating beam on to a sample at an oblique angle of incidence predetermined with reference to the sample surface. The light beam is reflected by the sample symmetrically relative to a normal to the sample surface. The reflected beam resulting from illumination of the sample is then directed on to a polarisation analysing device, whose output beam is detected before being processed. The changes in state of polarisation in phase and in amplitude brought about by reflection on the sample are processed in order to deduce physical parameters representing the sample.
In practice, the manufacture of integrated circuits comprises a plurality of stages of operation, some of which comprise the depositing of a plurality of successive layers. Most frequently, the depositing of these layers must be carried out without removing the sample from the depositing chamber, in particular in order to avoid breaching the controlled atmosphere of the chamber or contaminating the sample.
It is often necessary to measure physical parameters of one layer before the deposition or processing of the following layer.
A known solution consists in measuring in real time and in-situ the growth of the layers (or the etching) by means of an ellipsometric metrology apparatus.
Such a solution has the disadvantage of demanding as much ellipsometric metrology apparatus as deposition or processing chamber, which makes it relatively expensive.
Moreover, in certain processing stages of the layers (e.g. metal-coating stage), it is difficult or impossible, due to the optical absorption of the layers, to carry out such an ellipsometric solution.
Finally, it is virtually impossible to complete a cartography of the sample without removing the sample from the chamber and/or moving the sample relative to the illuminating beam, which is sometimes difficult to carry out in a chamber due to the limited dimensions of the chamber or the difficulty of incorporating inside the chamber a sample carrier which is movable along the X, Y and/or Z axis.
The present invention overcomes problems outlined above.
It thus has the main object of integrating an ellipsometric metrology in a chamber, without removing the sample from said chamber in order to measure the sample, e.g. between two manufacturing stages or at the end of one thereof, without contaminating the integrated circuits during manufacture and/or without breaching the controlled atmosphere of the chamber.
To this end, the present invention relates to a method of ellipsometric metrology for a sample contained in a chamber.
According to one important feature of the invention, the method comprises the following stages:
a) to provide a light source outside the chamber to produce an illuminating beam;
b) to provide a polarising device outside the chamber to polarise the illuminating beam;
c) to provide a window of selected dimensions and features and disposed in a plane substantially parallel to the surface of the sample and closing at least partly the chamber;
d) to direct the polarised illuminating beam on to the sample along a first optical path extending from the polarising device to the sample through the window, the first optical path forming a predetermined oblique angle of incidence relative to the sample surface;
e) to produce a reflected beam resulting from the illumination of the sample by the said illuminating beam, the reflected beam being symmetrical to the illuminating beam relative to a normal to the sample surface;
f) to provide a polarisation analysing device outside the chamber;
g) to focus the reflected beam on the analysing device along a second optical path extending from the sample to the analysing device through the window;
h) to detect the output beam emerging from the analysing device in order to supply an output signal;
i) to process the output signal in order to determine the changes in state of polarisation in phase and in amplitude caused by the reflection on the area of the sample.
The method according to the invention thus makes it possible to carry out an ellipsometric measurement of the sample without removing the same from the chamber, which avoids any problems of contamination, in particular during the manufacture of integrated circuits. The method according to the invention also has the advantage of not breaching the controlled atmosphere of the chamber. Moreover, the window permits an operator, if necessary by means of a microscope, to position precisely the illuminating beam on the sample.
The present invention has the further object of an ellipsometric metrology permitting the realisation of a cartography of the sample without removing the same from the chamber and without moving the sample.
To this end, the method according to the invention comprises furthermore a stage j) which consists in keeping the sample fixed in the chamber, and in moving longitudinally and/or laterally the polarised illuminating beam in order to illuminate another area of the sample, and in repeating the stages d) to I) at the same oblique angle of incidence.
The stage j) thus makes it possible to carry out a plurality of ellipsometry steps on a plurality of areas of the sample without moving the sample and without removing the sample from the chamber. Thus a cartography of the sample is obtained without problems of realisation, without causing contamination and without breaching the controlled atmosphere of the chamber.
Advantageously, the stage j) consists furthermore in moving transversely the illuminating beam on the fixed sample, through the window, in order to adjust the distance between the metrology apparatus and the sample surface.
Preferably, the method further comprises a stage of calibration in which the following stages are carried out:
1) to carry out at least a first ellipsometric measurement on a predetermined sample, according to first experimental conditions, without a window,
2) to carry out at least a second ellipsometric measurement on the same sample as that of stage 1), according to second experimental conditions similar to the first experimental conditions, but through the window,
3) to determine from the first and second ellipsometric measurements the effect resulting from the window on the relationship of the tangential amplitudes "PHgr" of the perpendicular and parallel polarisations of the reflected beam in order to deduce therefrom a correction factor; and
4) to take into account in the processing according to stage I) the correction factor thus deduced.
The present invention also has as an object an ellipsometric metrology apparatus for carrying out the method according to the invention.
A further object of the present invention is a chamber forming a box for holding a sample and comprising an interface with a window of selected dimensions and features disposed in a plane substantially parallel to the sample surface and at least partly closing the box, the box being intended to be associated with a metrology apparatus as described above.
Further features and advantages of the invention will appear from the detailed description below and from the drawings.